In vitro and in vivo induction and activation of nNOS by LPS in oligodendrocytes.

There are currently four known isoforms of nitric oxide synthase (NOS). Of these, neuronal NOS (nNOS) is known to be present exclusively in neurons, endothelial NOS (eNOS) in vascular endothelium, while the inducible form of NOS (iNOS) is known to be activated in oligodendrocytes, astrocytes and microglia. The fourth isoform, mitochondrial NOS (mtNOS), represents a post-translational modification of nNOS. Using western blotting and real time-PCR, we show induction and activation of nNOS following culture of oligodendrocyte progenitor cells (OPC) with lipopolysaccharide (LPS). Activation of nNOS results in accumulation of peroxynitrite and tyrosine nitration of proteins in oligodendrocytes resulting in reduced cell viability. Injection of LPS in vivo into the corpus callosum of rats leads to the development of extensive demyelination of the white matter tracts. Immunostaining of regions close to the injection site shows the presence of nNOS, but not iNOS, in oligodendrocytes. Neither iNOS nor nNOS was seen in astrocytes in areas of demyelination. These studies suggest that activation of nNOS in oligodendrocytes leads to oligodendrocyte injury resulting in demyelination.

Early degenerative changes in transgenic mice expressing mutant huntingtin involve dendritic abnormalities but no impairment of mitochondrial energy production.

Mitochondrial defects, which occur in the brain of late-stage Huntington's disease (HD) patients, have been proposed to underlie the selective neuronal loss in the disease. To shed light on the possible role of mitochondrial energy impairment in the early phases of HD pathophysiology, we carried out Golgi impregnation and quantitative histochemical/biochemical studies in HD full-length cDNA transgenic mice that were symptomatic but had not developed to a stage in which neuronal loss could be documented. Golgi staining showed morphologic abnormalities that included a significant decrease in the number of dendritic spines and a thickening of proximal dendrites in striatal and cortical neurons. In contrast, measurements of mitochondrial electron transport Complexes I-IV did not reveal changes in the striatum and cerebral cortex in these mice. Examination of the neostriatum and cerebral cortex in human presymptomatic and pathological Grade 1 HD cases also showed no change in the activity of mitochondrial Complexes I-IV. These data suggest that dendritic alterations precede irreversible cell loss in HD, and that mitochondrial energy impairment is a consequence, rather than a cause, of early neuropathological changes.

Fluorescence microscopy of stimulated Zn(II) release from organotypic cultures of mammalian hippocampus using a carbonic anhydrase-based biosensor system.

We demonstrate here that electrical stimulation of organotypic cultures of rat hippocampus results in the prompt release of significant amounts of Zn(II) by a fluorescence microscopic method. The fluorescence imaging of free Zn(II) is achieved using a highly selective biosensing indicator system consisting of human apo-carbonic anhydrase II (apoCAII) and a fluorescent aryl sulfonamide inhibitor of the enzyme, ABD-N. The apoenzyme and ABD-N in the absence of Zn(II) exhibit weak, reddish fluorescence typical of the ABD-N alone; when Zn(II) is added it binds to the apoenzyme (K(D) = 4 pM), which strongly promotes binding of ABD-N to the holoenzyme (K(D) = 0.9 microM). Binding of ABD-N to the holoenzyme results in a 9-fold increase in apparent quantum yield, significant blue shifts in excitation and emission, an increase in average fluorescence lifetime, a 4-fold increase in the ratio of intensities at 560 and 680 nm, and a large increase in anisotropy. Prior to stimulation, cultures immersed in phosphate-buffered saline with glucose and apoCAII with ABD-N emitted negligible fluorescence, but within 20 s after electrical stimulation a diffuse cloud of greenish fluorescence emerged and subsequently covered most of the culture, indicating release of zinc into the extracellular medium.

Transgenic mice expressing mutated full-length HD cDNA: a paradigm for locomotor changes and selective neuronal loss in Huntington's disease.

Huntington's disease (HD) is a progressive neurodegenerative disorder characterized clinically by motor and psychiatric disturbances and pathologically by neuronal loss and gliosis (reactive astrocytosis) particularly in the striatum and cerebral cortex. We have recently created HD full-length cDNA transgenic mouse models that may serve as a paradigm for HD. A more detailed characterization of these models is presented here. The transgene encoding normal huntingtin consists of 9417 bp of the huntingtin coding sequences including 16 tandem CAGs coding for polyglutamines as part of exon 1. The transgene is driven by a heterologous cytomegalovirus promoter. Five independent transgenic mouse lines were obtained using this construct. An additional six transgenic lines were obtained using full-length HD constructs that have been modified to include either 48 or 89 CAG repeat expansions. Southern blot and densitometric analyses indicated unique integration sites for the transgene in each of the lines with a copy number ranging from two to 22 copies. Widespread expression of the transgene in brain, heart, spleen, kidney, lung, liver and gonads from each line was determined by Western blot analyses. In the brain, transgene expression was found in cerebral cortex, striatum, hippocampus and cerebellum. Expression of the transgene was as much as five times the endogenous mouse huntingtin level. Phenotypically, only mice expressing 48 or 89 CAG repeats manifested progressive behavioural and motor dysfunction. Early behavioural abnormalities were characterized by trunk curling and clasping of both fore- and hindlimbs when the animals were suspended by their tails. Subsequently, these mice exhibited hyperkinetic movements, including heightened exploratory activities, unidirectional rotational behaviour, backflipping and excessive grooming that lasted for several weeks. Eventually, the animals progressed to a hypokinetic phase consisting of slowed movements and lack of response to sensory stimuli. Urine retention or incontinence was also a prominent feature of the hypokinetic phase. At the end stage of the disease process, HD48(B,D) and HD89(A-C) mice became akinetic just prior to death. Neuropathological examination of mice at various stages indicated that it was only during the hypokinetic phase and thereafter when selective neuronal loss was most apparent. Regions of neurodegeneration and loss included the striatum, cerebral cortex, thalamus and hippocampus. TUNEL staining indicated an apoptotic mode of cell death in these brain regions. Comparative neuronal counts after Nissl staining showed as much as 20% loss of small and medium neurons in the striatum in mice at the hypokinetic and akinetic stages. Reactive astrocytosis accompanied the areas of neurodegeneration and loss. Polyglutamine aggregates in the form of neuronal intranuclear inclusions and diffuse nuclear and perinuclear aggregations were found in a small percentage of neurons, including those in brain regions that are typically spared in HD. This observation suggests that polyglutamine aggregates may not be sufficient to cause neuronal loss in HD. In both behavioural and neuropathological analyses, wild-type and transgenic animals with 16 CAG repeats were indistinguishable from each other and do not exhibit the changes observed for mice carrying the 48 and 89 CAG repeat mutations. Thus, animals expressing the CAG repeat expansions appear to represent clinically analogous models for HD pathogenesis, and may also provide insights into the underlying pathophysiological mechanisms of other triplet repeat disorders.

Behavioural abnormalities and selective neuronal loss in HD transgenic mice expressing mutated full-length HD cDNA.

Huntington disease (HD) is an adult-onset, autosomal dominant inherited human neurodegenerative disorder characterized by hyperkinetic involuntary movements, including motor restlessness and chorea, slowing of voluntary movements and cognitive impairment. Selective regional neuron loss and gliosis in striatum, cerebral cortex, thalamus, subthalamus and hippocampus are well recognized as neuropathological correlates for the clinical manifestations of HD. The underlying genetic mutation is the expansion of CAG trinucleotide repeats (coding for polyglutamines) to 36-121 copies in exon 1 of the HD gene. The HD mRNA and protein product (huntingtin) show widespread distribution, and thus much remains to be understood about the selective and progressive neurodegeneration in HD. To create an experimental animal model for HD, transgenic mice were generated showing widespread expression of full-length human HD cDNA with either 16, 48 or 89 CAG repeats. Only mice with 48 or 89 CAG repeats manifested progressive behavioural and motor dysfunction with neuron loss and gliosis in striatum, cerebral cortex, thalamus and hippocampus. These animals represent clinically relevant models for HD pathogenesis, and may provide insights into the underlying pathophysiological mechanisms of other triplet repeat disorders.

Neurotoxicity of endogenous cysteinylcatechols.

Progression of Parkinson's disease has been associated with several biochemical changes in the substantia nigra including increased oxidative challenge, catechol oxidation, and inhibition of mitochondrial complex I activity. Cysteinylcatechols, formed by nucleophilic addition of cysteine to oxidized catechols, have been identified as markers of catechol oxidation in brain tissue. We have examined the neurotoxicity of a series of cysteinylcatechols. Of the compounds examined, only 5-S-cysteinyl-3,4-dihydroxyphenylacetate (cysdopac) was specifically cytotoxic to differentiated P19 neuroglial cultures. Cysdopac also was neurotoxic to pyramidal neurons in organotypic cultures of hippocampus, and this effect was ablated by selective N-methyl-D-aspartate (NMDA) receptor antagonists. In vitro, cysdopac was a potent inhibitor of mitochondrial complex I activity. However, electrophysiologic experiments failed to demonstrate NMDA receptor agonist activity for cysdopac, nor did cysdopac inhibit glutamate uptake. These results showed that cysdopac was the most potent neurotoxin of this series of cysteinylcatechols and suggest that cysdopac may function as an indirect excitotoxin, potentially via inhibition of mitochondrial respiration.

Immunohistochemical detection of 4-hydroxy-2-nonenal adducts in Alzheimer's disease is associated with inheritance of APOE4.

Cumulative oxidative damage, including lipid peroxidation, is a central component of cellular aging and is thought to play a role in the pathogenesis of late-onset Alzheimer's disease (AD). Lipid peroxidation produces several cytotoxic aldehydes, one of the most potent being 4-hydroxy-2-nonenal (HNE). We have shown previously that HNE is a potent neurotoxin that covalently modifies and cross-links neuronal cytoskeletal protein in neuroglial cultures, suggesting that HNE may contribute to the pathogenesis of AD. In addition to aging, inheritance of the epsilon 4 allele of APOE is the other major risk factor for development of late-onset AD; however, the mechanisms through which aging and apolipoprotein E isoforms may collaborate in the onset or progression of AD are not known. We tested the hypothesis that HNE may yield a particular type of protein modification, pyrrole adduction, and that this may contribute to the pathogenesis of AD. Our data demonstrated that HNE formed pyrrole adducts with protein. Polyclonal antiserum was raised that specifically recognized HNE pyrrole adducts, and immunohistochemical analysis was performed on hippocampus and temporal cortex of 10 patients with histologically verified AD. Pyramidal neuron cytoplasm was immunoreactive in 4 of 4 APOE4 homozygotes, 2 of 3 APOE3/4 heterozygotes, and none of 3 APOE3 homozygotes (P < 0.05). The pattern of staining was highly suggestive of neurofibrillary tangles as the primary immunoreactive structure. These data suggest that differences in neuronal protein modification by HNE may account in part for the APOE-associated stratification of risk for late-onset AD.

Attenuation of 1-methyl-4-phenylpyridinium (MPP+) neurotoxicity by deprenyl in organotypic canine substantia nigra cultures.

Systemic administration of MPTP to experimental animals induces neurodegeneration of dopaminergic neurons in the central nervous system. MPTP crosses the blood-brain barrier where it is taken up by astrocytes and converted to MPP+ by monamine oxidase-B (MAO-B). Subsequently, MPP+ is selectively taken up by dopaminergic neurons upon which it exerts intracellular neurotoxic effects. Systemic administration of the selective MAO-B inhibitor deprenyl prevents the conversion of MPTP to MPP+ and by this mechanism is able to protect against MPTP neurotoxicity. Deprenyl has also been reported to exert neuroprotective effects that are independent of its MAO-B inhibitory properties, but since MPP+ itself does not cross the blood-brain barrier it is difficult to directly study the MAO-B independent in vivo effects of MPP+ itself. One approach is to use organotypic tissue cultures of the canine substantia nigra (CSN) which permit administration of precise concentrations of pharmacological agents directly to mature, well-developed and metabolically active dopaminergic neurons. These neurons as well as other components of the cultures exhibit morphological and biochemical characteristics identical to their in vivo counterparts. This study was undertaken to evaluate the neuroprotective effects of deprenyl in MPP(+)-treated cultures by measuring changes in the levels of HVA as an indicator of dopamine release and metabolism by dopaminergic neurons and to correlate this indication of dopaminergic function with morphological evidence of survival or loss of dopaminergic neurons in mature CSN cultures. Mature CSN cultures, at 44 days in vitro (DIV), were exposed to either MPP+ alone, deprenyl alone or simultaneously to both deprenyl and MPP+ or to MPP+ following 4 day pretreatment with deprenyl. Exposure to MPP+ alone caused significant reduction in HVA levels, evidence of widespread injury and ultimate disappearance of large neurons in the cultures. These effects were attenuated by simultaneous exposure to MPP+ and deprenyl and the destructive effects of MPP+ appeared to be prevented by pretreatment with deprenyl. Thus the neuroprotective effects of deprenyl on MPP(+)-induced reduction of HVA levels in living cultures appears similar to the effects of deprenyl on dopamine levels and tyrosine hydroxylase activity reported by others in cultures previously exposed to deprenyl and MPP+. These studies also confirm that the neuroprotective effects of deprenyl against MPP+ in dopaminergic neurons are, at least in part, independent of deprenyl's inhibition of MAO-B.

Neurochemical and metabolic consequences of elevated cerebrospinal fluid quinolinic acid concentrations in rat brain.

Quinolinic acid (QUIN) is an endogenous excitatory amino acid, which is elevated in brain tissues or cerebrospinal fluid (CSF) in several acute and chronic inflammatory central nervous system (CNS) diseases. The functional significance of this elevation is unknown but speculations of excitotoxicity have been raised. We have begun to address the pathologic consequences of elevated CSF QUIN by studying the effects of intracerebroventricular (i.cv) administration of QUIN on regional choline acetyltransferase (ChAT) activity, somatostatin content and glucose metabolism in the rat brain. QUIN (12 and 60 nmol) i.cv administration once a day for 7 days (total dose; 84 and 420 nmol, respectively) had minimal effect on somatostatin content and no effect on ChAT activity. In contrast, following continuous i.cv infusion of QUIN for 14 days using an osmotic minipump (480 nmol), ChAT activity dropped in the hippocampus and the striatum and somatostatin content was reduced in the frontal cortex, hippocampus, striatum and amygdala. Moreover, following the QUIN infusion, glucose utilization decreased in the basal nucleus of Meynert, frontal cortex, and portions of the basal ganglia and the limbic system. These results indicate that subchronic i.cv infusion of QUIN to rats results in selective regional neurochemical and metabolic changes distributed throughout the CNS. These results suggest target brain areas and transmitter systems which may be associated with neurologic syndromes characterized by elevated CSF QUIN levels.

Quantitative analysis of the toxicity of human amniotic fluid to cultured rat spinal cord.

It has been proposed that the myelodysplastic components of a myelomeningocele are secondarily damaged as the result of exposure to amniotic fluid, the so-called 'two-hit' hypothesis. The critical time at which this secondary insult might occur has not been clearly defined. The present study addresses this issue by quantitatively assessing the toxic effects of human amniotic fluid of various gestational ages upon organotypic cultures of rat spinal cord. Using an assay for lactate dehydrogenase efflux to evaluate toxicity in such spinal cord cultures, we found that the amniotic fluid became toxic at approximately 34 weeks' gestation. This toxic effect of amniotic fluid appears to emerge rather suddenly. Accordingly, it seems reasonable to suggest that prevention of exposure of vulnerable spinal cord tissue to this toxicity by surgical closure of a myelomeningocele defect prior to the emergence of toxicity in amniotic fluid may prevent injury to vulnerable myelodysplastic spinal cord tissue.

Intravascular malignant lymphoma ("malignant angioendotheliomatosis") mimicking primary angiitis of the central nervous system.

Malignant angioendotheliomatosis is characterized by the plugging of central nervous system blood vessels with large mononuclear cells, thus mimicking primary angiitis of the central nervous system. When autoantibodies are present, it can mimic connective tissue disease. Treatment of malignant angioendotheliomatosis with cytoxan may prolong survival.

Dysfunction of brain kynurenic acid metabolism in Huntington's disease: focus on kynurenine aminotransferases.

The levels of the neuroprotective excitatory amino acid receptor antagonist kynurenic acid (KYNA) have been previously shown to be reduced in several regions of the brain of Huntington's disease (HD) patients. Thus, KYNA has been speculatively linked to the pathogenesis of HD. We have examined KYNA levels and the activity of its two biosynthetic enzymes (kynurenine aminotransferases (KAT) I and II) in 12 regions of brains from late-stage HD patients and control donors (n = 17 each). KYNA levels were measured in the original tissue homogenate. Using [3H]kynurenine as the substrate, enzyme activities were determined in dialyzed tissue homogenates. KYNA levels in the caudate nucleus decreased from 733 +/- 95 in controls to 401 +/- 62 fmol/mg tissue in HD (p < 0.01). The activity of both enzymes was highest in cortical areas (e.g. control frontal cortex: KAT I: 148 +/- 18 fmol/mg tissue/h; KAT II: 25 +/- 2 fmol/mg tissue/h). The activities of both KAT I and KAT II, when expressed per mg original weight, showed significant decreases (48-55%) in the HD putamen (p < 0.01). Trends toward lower enzyme activities and KYNA concentrations were detected in other brain areas as well. Kinetic analyses, performed in putamen and cerebellum, showed an approximately 3-fold increase in Km values for both KAT I and KAT II in the putamen only. Vmax values remained unchanged in the HD brain. These findings indicate a selective impairment in KYNA biosynthesis in the neostriatum of HD patients, possibly due to the loss of (an) endogenous KAT activator(s).(ABSTRACT TRUNCATED AT 250 WORDS)

Global aphasia with seizure onset in the dominant basal temporal region.

A 33-year-old right-handed woman had intractable simple and complex partial seizures (SPS, CPS) that began with global aphasia. EEG closed-circuit TV (EEG-CCTV) monitoring with sphenoidal electrodes showed left inferomesial temporal ictal onset of CPS. Subdural electrodes were implanted over the left frontotemporal convexity, subtemporally and subfrontally. Stimulation of the basotemporal cortex produced global aphasia. A posterolaterotemporal language area was also identified. Spontaneous SPS had focal onset in the basal temporal language area (BTLA). Ictal discharges did not involve the posterotemporal region. This case shows that aphasic speech arrest at seizure onset may be due to seizure discharge in the basotemporal region and that the BTLA is clinically relevant in seizure semiology.

Baroreflex failure in a patient with central nervous system lesions involving the nucleus tractus solitarii.

Animal studies have shown the importance of the nucleus tractus solitarii, a collection of neurons in the brain stem, in the acute regulation of blood pressure. Impulses arising from the carotid and aortic baroreceptors converge in this center, where the first synapse of the baroreflex is located. Stimulation of the nucleus tractus solitarii provides an inhibitory signal to other brain stem structures, particularly the rostral ventrolateral medulla, resulting in a reduction in sympathetic outflow and a decrease in blood pressure. Conversely, experimental lesions of the nucleus tractus solitarii lead to loss of baroreflex control of blood pressure, sympathetic activation, and severe hypertension in animals. In humans, baroreflex failure due to deafferentation of baroreceptors has been previously reported and is characterized by episodes of severe hypertension and tachycardia. We present a patient with an undetermined process of the central nervous system characterized pathologically by ubiquitous infarctions that were particularly prominent in the nucleus tractus solitarii bilaterally but spared the rostral ventrolateral medulla. Absence of a functioning baroreflex was evidenced by the lack of reflex tachycardia to the hypotensive effects of sodium nitroprusside, exaggerated pressor responses to handgrip and cold pressor test, and exaggerated depressor responses to meals and centrally acting alpha 2-agonists. This clinicopathological correlate suggests that the patient's baroreflex failure can be explained by the unique combination of the destruction of sympathetic inhibitory centers (ie, the nucleus tractus solitarii) and preservation of centers that exert a positive modulation on sympathetic tone (ie, the rostral ventrolateral medulla).

Thiamine utilization in the pathogenesis of alcohol-induced brain damage.

There is increasing evidence for the role of thiamine deficiency in ethanol neurotoxicity and in development of alcoholic organic brain disorders other than Wernicke-Korsakoff syndrome [WKS] and cerebellar degeneration. Investigations in humans and in animal models have implicated a reduction in the activities of thiamine-utilizing enzymes as the metabolic basis of tissue injury due to thiamine deficiency. We have investigated the interactions of the thiamine-utilizing enzyme transketolase [Tk], derived from human fibroblasts, lymphoblasts, and various brain regions, with its cofactor, thiamine pyrophosphate [TPP], in an attempt to elucidate the molecular basis of selective brain damage in alcoholism-associated thiamine deficiency. There were no significant differences in the isoelectric pattern of Tk among the nine brain regions (white matter and grey matter) examined. However, Tk activity/mg protein, increase in Tk activity with addition of excess TPP (TPP effect), and TPP-dependent rate of formation of active Tk holoenzyme (tau) varied 2.5-, 6-, and 4-fold, respectively, among these brain regions. These differences in tissue requirements for TPP may contribute to the selective vulnerability of certain brain regions to alcoholism-associated thiamine deficiency, and may influence the pattern of clinical impairment in the individual patient.

Preferential neuronal loss in layer III of the entorhinal cortex in patients with temporal lobe epilepsy.

We report a characteristic pattern of neuropathological change in the entorhinal cortex (EC) from four patients with temporal lobe epilepsy. Specimens of the EC were obtained during the surgical treatment of intractable partial seizures and were studied by light microscopy in Nissl-stained sections. A distinct loss of neurons was observed in the anterior portion of the medial EC in the absence of apparent damage to temporal neocortical gyri. Cell loss was most pronounced in layer III, but also noticed in layer II, particularly in the rostral field. A similar pattern of neurodegeneration in the EC was found in all specimens examined though the degree of neuronal loss varied between cases. These observations provide neuropathological evidence for an involvement of the EC in temporal lobe epilepsy. Since the EC occupies a pivotal position in gating hippocampal input and output, our results further support previous suggestions that dysfunction of this region may contribute, either independently or in concert with Ammon's horn sclerosis, to epileptogenesis in humans.

Identification of extrastriatal dopamine D2 receptors in post mortem human brain with [125I]epidepride.

The regional distribution of striatal and extrastriatal dopamine D2 receptors in human brain was studied in vitro with (S)-N-[(1-ethyl-2- pyrrolidinyl)methyl]-5-[125I]iodo-2,3-dimethoxybenzamide, [125I]epidepride, using post mortem brain specimens from six subjects. Scatchard analysis of the saturation equilibrium binding in twenty-three regions of post mortem brain revealed highest levels of binding in the caudate (16.5 pmol/g tissue) and putamen (16.6 pmol/g tissue) with lower levels seen in the globus pallidus (7.0 pmol/g tissue), nucleus accumbens (7.2 pmol/g tissue), hypothalamus (1.8 pmol/g tissue), pituitary (1.3 pmol/g tissue), substantia innominata (1.0 pmol/g tissue), and amygdala (0.87 pmol/g tissue). Of note was the presence of dopamine D2 receptors in the four thalamic nuclei studied, i.e. anterior nucleus (1.0 pmol/g tissue), dorsomedial nucleus (0.96 pmol/g tissue), ventral nuclei (0.72 pmol/g tissue), and pulvinar (0.86 pmol/g tissue), at levels comparable to the amygdala (0.87 pmol/g tissue) and considerably higher than levels seen in anterior cingulate (0.26 pmol/g tissue) or anterior hippocampus (0.36 pmol/g tissue). The frontal cortex had very low levels of dopamine D2 receptors (0.17-0.20 pmol/g tissue) while the inferior and medial temporal cortex had relatively higher levels (0.31-0.46 pmol/g tissue). Inhibition of [125I]epidepride binding by a variety of neurotransmitter ligands to striatal, ventral thalamic and inferior temporal cortical homogenates demonstrated that [125I]epidepride binding was potently inhibited only by dopamine D2 ligands. The present study demonstrates that dopamine D2 receptors are present in basal ganglia, many limbic regions, cortex and in the thalamus. The density of thalamic D2 receptors is comparable to many limbic regions and is considerably higher than in cortex.(ABSTRACT TRUNCATED AT 250 WORDS)

Cochleovestibular nerve compression syndrome. II. Vestibular nerve histopathology and theory of pathophysiology.

The present study was undertaken to systematically examine and characterize pathological changes in vestibular nerve specimens obtained at surgery in patients with symptomatic cochleovestibular nerve compression syndrome (CNCS). Vestibular nerves were obtained in six cases of CNCS and were intermingled with vestibular nerves obtained in cases of Meniere's disease. All of the nerve specimens were coded and reviewed microscopically in a blind-study fashion by the neuropathologist. The vestibular nerves obtained from CNCS cases showed significant endoneurial fibrosis, compared to controls (specimens from patients with Meniere's disease). Based on observations in this study, as well as the clinical symptoms and audiovestibular test findings in these patients, a theory of pathophysiology in CNCS of the cochleovestibular nerve is proposed. The implications of this theory are discussed with respect to the diagnosis of CNCS.